So I'm a bit late about this...
So I'll start with the races. Since its about races, I'm going to leave Humans for last. I'll also only cover Forgotten Realms and PHB races as PHB2 covers many new races as well as some from Dragon Magazines (that will probably come out in Eberon or PHB3). Due to the fact that there could be copyright issues for me putting stuff directly from the book, I won't put alot of info.
Dragonborn
You look dragon-esque, your tall, can be leaned more towards warlords, fighters, and paladin classes. Surprising for the paladin, yes? Well that is because of their beliefs being high. They also speak Draconic (that means Dragon speak people).
Dwarf
Short creatures who have many benefits. They lean towards paladins, clerics, and fighter classes. They always can move 25 feet (5 squares) even when encumbered so they can lug the weight but makes them the slowest among the races. They can see in low-light.
Drow (Forgotten Realms type)
They can see in the dark (not low light, DARK). They are like decendents of Eladrins, but they are deadlier as they usually don't favor the side of good. Plus they can be scary. They usually will lean to Rangers, rogues, and Warlocks.
Genasi (Forgotten Realms Type)
Elemental origin type creatures. They can be any type of element of the listed in the books. They highly favor Swordmages, but can also major in warlord. They get another encounter power depending on their element they are and can have multiple elements. There are 5 elements. Each element has its own bonus as well.
Eladrin
Graceful and intelligent and are of Fey origins. They lean towards wizard, rogue, and warlord types, but can also be Swordmages since intelligence is a key basis. They can see in low-light also.
Elf
Are of Fey origin like Eladrin, but in terms of higher ups, Elf is lower than Eladrin. Can favor the ranger, rogue, and cleric classes. They help others in perception easily and they ignore difficult terrain. They are also the fastest in movement speed. They can see in low-light.
Half-Elf
They aren't like Elves in terms of fey origin. They aren't like Human's either. They offer diplomacy checks that increase to others around them, can have 3 languages (2 racial which would be common and elven and a 3rd one of their choosing). The benefit of being 2 different races at the same time for their heritage, they can get feats for both Elf, Human and even feats for half-elf's only. Makes you versatile. Besides, they can even see in low-light. They favor more on Warlord, Paladin, and Warlock classes.
Halfling
Think of them as munchkins. They can have 2 languages, the common language and a language of their choosing. They are short though and they usually are the brave ones. Surprisingly, their speed is not affected.
Tiefling
Demonic type creatures in a sense. They can be any alignment, can see in low-light, and have the best abilities to be either Warlock, Warlord, or Rogue classes, but they could also do Swordmage since they have intelligence in their key ability bonuses. Though, this doesn't mean they aren't limited to just those classes, but it is more of a chance for them to be that way.
Human
Ah, a human. The most versatile of everyone. They are much more short-lived so they get more bonuses than other races in terms of: Powers, 1 more language besides common, another feat at 1st level, another training in a skill that is part of their class list. They can do any class since they only have a +2 to 1 ability score, hence their main or second abilities will always be good depending on what they need. Plus, they get a bonus to ALL defenses.
I guess I will do a part 4 on example character to complete the guide.